1. Field of the Invention
The present invention relates to a method for producing a rotor laminated core in which permanent magnets are provided in magnet-insertion holes, and particularly relates to a method for producing the rotor laminated core that reduces magnetic flux loss.
2. Description of the Related Art
In recent years, an electric motor which uses permanent magnets for a rotor is used for a hybrid car, an electric car, an air-conditioner, and the like. The permanent magnets are inserted in a plurality of magnet-insertion holes formed along the circumference of the rotor laminated core. However, since it is general that the magnet-insertion hole only has a space slightly larger than the shape of the eternal magnet which is inserted in the magnet-insertion hole, leakage flux which passes the laminated core in magnetic flux directing from the N pole to the S pole of the permanent magnet may be generated.
Thus, as described in JP-A-9-289745, it is proposed that a groove-shaped hardened part is provided by compression transformation in a bridge part in which the magnetic flux is leaked out from the N pole to the S pole of the permanent magnet in a lateral side of the permanent magnet. It is described that the leakage flux decreases, and the strength of the laminated core is improved by providing the hardened part. These aspects are shown in a plan view of FIG. 8A and a side view of FIG. 8B. FIG. 8A and FIG. 8B illustrate a magnet-insertion hole 71, a hardened part (thinning part) 72 and a bridge part (an area A through which leakage flux passes) 73.
The method for producing a rotor laminated core in this case is described referring to FIGS. 9A to 9D. In a core piece 60 which constitute a part of the rotor laminated core, as shown in FIG. 9A, a plurality of magnet-insertion holes 61 arranged along a circumferential direction are formed at an outside area in a radial direction of the core piece 60. Then, a coining process is performed to form a thinning part 62 as shown in FIG. 9B, and an outer shape of the core piece 60 is punched as shown in FIG. 9C, thereby forming each core piece 60. In FIGS. 9B and 9C, a bridge part 63 is shown.